Multiple sclerosis (MS) is an inflammatory and degenerative disease of the central nervous system (CNS) with diverse clinical presentations and heterogeneous histopathological features. Understanding the neuropathology of MS is essential to develop improved therapies. MS lesions or “plaques” in the CNS white matter have distinct histological and immunocytological characteristics depending on disease activity. This heterogeneity implies that there are discrete molecular events at different pathogenetic stages of MS. Therefore, identification of targets specific to pathological types of MS lesions may have therapeutic benefits during different stages of disease.
For example, Lucchinetti et al. (2000) Annals of Neurology 47(6):707-717 determined four patterns of disease into which MS lesions fit. All had inflammatory infiltrates by T lymphocytes and macrophages in common but segregated on the basis of plaque geography, distribution of myelin protein loss, evidence of immunoglobulin and complement deposition, and oligodendrocyte death.
Although patterns of demyelination were heterogeneous between patients, multiple lesions within a patient all manifested the same phenotype, suggesting that lesion patterns are distinct mechanisms present in subgroups of MS patients. Understanding the pathogenetic mechanisms in demyelinating lesions has significant implications for developing and implementing appropriate therapies. In particular, understanding the relative loss or sparing of oligodendrocytes will determine what therapeutic strategies have potential efficacy in an individual MS patient.
In MS, myelin reactive T cells enter into the brain and spinal cord and mediate destruction of the myelin sheath surrounding neurons resulting in progressive motor dysfunction and eventual paralysis. Current treatment strategies include switching the pro-inflammatory Th1 T cell phenotype to an anti-inflammatory Th2 response, preventing encephalitogenic T cells from extravasating into the brain, inducing T cell tolerance, anergy or apoptosis, and repairing or replacing damaged CNS cells, such as neurons and oligodendrocytes.
Goals for therapy include shortening acute exacerbations, decreasing frequency of exacerbations, and relieving symptoms; maintaining the patient's ability to walk is particularly important. Acute exacerbations may be treated with brief courses of corticosteroids. However, although they may shorten acute attacks and perhaps slow progression, corticosteroids have not been shown to affect long-term outcome.
Immunomodulatory therapy decreases frequency of acute exacerbations and delays eventual disability. Immunomodulatory drugs include interferons (IFNs), such as IFN-β1b and IFN-β1a. Glatiramer acetate may also be used. Other potential therapies include the immunosuppressant methotrexate and Natalizumab, an anti-α4 integrin antibody that inhibits passage of leukocytes across the blood-brain barrier. Immunosuppressants such as mycophenolate and cyclophosphamide have been used for more severe, progressive MS but are controversial.
In addition to suppressing the pathological immune response it is important to protect CNS cells from further damage and to induce repair of injured cells since some cells such as neurons have few progenitors in the adult mammalian brain and are thus limiting.
Limited therapeutic benefit achieved with the above-mentioned immunotherapies may relate to the apparent pathogenetic and clinical heterogeneity of MS. An improved understanding of the pathologic processes involved may allow therapies to be targeted to subgroups of MS patients that are most likely to respond. Clearly, in order to tailor therapy for each patient, classification of pathogenetic mechanism, preferably by using noninvasive methods, will be necessary.
In recent years, a “systems biology” approach using large-scale analysis of proteins and gene transcripts has illuminated new aspects of pathogenesis for complex disease networks including malignancies, neurodegenerative disorders and infections. Similarly, large-scale transcriptional profiling of MS lesions has identified involvement of novel molecules and pathways such as osteopontin and Notch/Jagged signalling, respectively. However, transcriptomic analysis fails to provide a comprehensive understanding of effector molecules involved in MS pathogenesis due to the susceptibility of mRNA to degradation and the discrepancy between mRNA and protein expression levels. Transcriptomic analysis also overlooks signaling molecules from serum, hormones and neurotransmitters.
The present invention provides an alternative approach, where characterization of MS lesions utilized focused proteomic analysis, enriched by laser-capture microdissection (LCM) and analyzed by sensitive tools such as mass spectrometry, provides functional insights into MS pathogenesis.